But on 10 December 2007, the HTML5 specification was updated, replacing the reference to concrete formats:

Initially, Ogg Theora was the recommended standard video format in HTML5, because it was not affected by any known patents.

In addition to software decoders, a hardware video decoder should exist for the format, as many embedded processors do not have the performance to decode video.

Have good compression, good image quality, and low decode processor use.

The HTML5 Working Group considered it desirable to specify at least one video format which all user agents (browsers) should support. User agents are free to support any video formats they feel are appropriate, but content authors cannot assume that any video will be accessible by all complying user agents, since user agents have no minimal set of video and audio formats to support. The HTML5 specification does not specify which video and audio formats browsers should support.

The MIME type denotes the container format of the file, and the container format defines the interpretation of the codec string. The 'type' attribute specifies the MIME type and possibly a list of codecs, which helps the browser to determine whether it can decode the file without beginning to download it. Alternatively, the JavaScript canPlayType() function can be used to achieve the same. Using any number of elements, as shown below, the browser will choose automatically which file to download. The 'video' element supports fallback through specification of multiple sources. The browser in question 'knows best' what formats it can use. For other features, browser sniffing is used sometimes, which may be error-prone: any web developer's knowledge of browsers will inevitably be incomplete or not up-to-date.

Video format support varies among browsers (see below), so a web page can provide video in multiple formats. Its purpose is to be representative of the video. The optional 'poster' attribute specifies an image to show in the video's place before playback is started. Alternatively, playback can be controlled with JavaScript, which the web designer can use to create a custom user interface. The 'controls' attribute enables the browser's own user interface for controlling playback. This is fallback content to display for user agents that do not support the video tag.

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